User demand has demonstrated a need for increasingly higher speed digital access in new office communication controllers as daily routines become more complex and greater demands are placed on improving productivity. Current Local Area Network (LAN) solutions that provide this higher speed are beset by high cost and congestion. Moreover, these solutions are usually poorly suited to integrating voice services.
An alternative to the traditional LAN approach is to integrate all voice and data services into a centralized controller and to utilize inexpensive standard in-building twisted pair wiring to provide the required interconnects. A commonly experienced problem in this approach is the restriction to low baud rates for transmission. Notwithstanding the limited transmission capability of standard twisted pair wiring, a viable centralized controller is expected to execute both ends of a 2.56 Mb/s digital line interface over such wiring.
Under these circumstances a common requirement is to equalize for InterSymbol Interference (ISI) which is caused by the bandwidth restrictions of the twisted pair wiring. Other line conditions may occur, however, which complicate the achievement of adequate equalization. Further complications arise as a result of ISI being adversely affected by both static and dynamic conditions. Mixed wire gauges, for example, constitute a static condition that may be compensated through fixed equalization. However, imperfect pre-equalization of line signals and itinerant bridged tap connections, which may also be transient, on the line present substantial problems in line equalization.